In recent years the theory that measurement of the potential level of the electromagnetic field of a living organism can be used as an accurate diagnostic tool is gaining greater acceptance. Many methods and devices have been developed in an attempt to implement this theory. For example, U.S. Pat. No. 4,328,809 to B.H. Hirschowitz et al deals with a device and method for detecting the potential level of the electromagnetic field present between a reference point and a test point of a living organism. Here, a reference electrode provides a first signal indicative of the potential level of the electromagnetic field at the reference point, while a test electrode provides a second signal indicative of the potential level of the electromagnetic field at the test point. These signals are provided to an analog-to-digital converter which generates a digital signal as a function of the potential difference between the two, and a processor provides an output signal indicative of a parameter or parameters of the living organism as a function of this digital signal.
Similar biopotential measuring devices are shown by U.S. Pat. No. 4,407,300 to Davis, and U.S. Pat. No. 4,557,271 and 4,557,273 to Stoller et al. Davis in particular discloses the diagnosis of cancer by measuring the electromotive forces generated between two electrodes applied to a subject.
Often, the measurement of biopotentials has been accomplished using an electrode array, with some type of multiplexing system to switch between electrodes in the array. The aforementioned Hirschowitz et al patent contemplates the use of a plurality of test electrodes, while U.S. Pat. No. 4,416,288 to Freeman and U.S. Pat. No. 4,486,835 to Bai disclose the use of measuring electrode arrays.
Unfortunately, previous methods for employing biopotentials measured at the surface of a living organism as a diagnostic tool, while basically valid, are predicated upon an overly simplistic hypothesis which does not provide an effective diagnosis for many disease states. Prior methods and the devices which implement them operate on the basis that a disease state is indicated by a negative polarity which occurs relative to a reference voltage obtained from another site on the body of a patient, while normal or non-malignant states, in the case of cancer, are indicated by a positive polarity. Based upon this hypothesis, it follows that the detection and diagnosis of disease states can be accomplished by using one measuring electrode situated on or near the disease site to provide a measurement of the polarity of the signal received from the site relative to that from the reference site. Where multiple measuring electrodes have been used, their outputs have merely been summed and averaged to obtain one average signal from which a polarity determination is made. This approach is subject to major deficiencies which lead to diagnostic inaccuracy.
First, the polarity of diseased tissue underlying a recording electrode has been found to change over time. This fact results in a potential change which confounds reliable diagnosis when only one recording electrode is used. Additionally, the polarity of tissue as measured by skin surface recording is dependent not only upon the placement of the recording electrode, but also upon the placement of the reference electrode. Therefore, a measured negative polarity is not necessarily indicative of diseases such as cancer, since polarity at the disease site depends in part on the placement of the reference electrode.
As disease states such as cancer progress, they produce local effects which include changes in vascularization, water content, and cell division rate. These effects alter ionic concentrations which can be measured at the skin surface. Other local effects, such as distortions in biologically closed electrical circuits, may also occur. A key point to recognize is that these effects do not occur uniformly around the disease site. For example, as a tumor grows and differentiates, it may show wide variations in its vascularity, water content and cell division rate, depending on whether examination occurs at the core of the tumor (which may be necrotic) or at the margins of the tumor (which may contain the most metabolically active cells). Once this fact is recognized, it follows that important electrical indications of disease are going to be seen in the relative voltages recorded from a number of sites at and near a diseased area, and not, as previously assumed, on the direction (positive vs. negative) of polarity.